This application relates to apparatus, systems, and techniques for optical communication.
Communication capacity in communication systems is valuable and various techniques have been developed and investigated to increase capacity of communication systems. In optical communications, spectrally-efficient optical communication techniques have been developed and investigated. Optical wavelength-division multiplexing (WDM), for example, can be used to increase the amount of data to be transmitted in a single fiber by simultaneously transmitting multiple optical WDM channels through the fiber. Dense WDM and ultradense WDM further increase the number of channels that can be carried in a single fiber.
One method for doubling the spectral efficiency and system capacity is polarization-division-multiplexing (PDM), in which two independently modulated data channels located at the same optical wavelength are simultaneously transmitted on orthogonal polarization states of the fiber. For systems with low polarization-mode-dispersion (PMD) and polarization-dependent-loss (PDL), PDM can be used for upgrading existing fiber links or for the deployment of spectrally-efficient new optical fiber systems.